Microbiota of GI tract Flashcards
Why does transit time affect bacterial populations in different parts of the GI tract
Due to different bacterial growth rates
Transit time of food in the mouth
1 min max
Transit time of food in the oesophagus
4-8 secs
Transit time of food in the stomach
2-4 hrs
Transit time of food in the LI
10 hrs - several days
As you go down the GI tract, there’s more…
Bacteria
Esp obligate anaerobes because less oxygen the further down you go
What are facultative anaerobes + where are they found + what pH they live in
Grow in presence and absence of oxygen
Found in the stomach, existing at pH 1.5 - 4
Name some facultative anaerobes
Lactobacillus
H.pylori
What are obligate anaerobes + where are they found + what pH they live in
Can’t grow in presence of oxygen
Found in the colon at pH 5.5 - 6.5
Name some obligate anaerobes
Bacteroides
Clostridium groups
Enterobacteraceae
pH of mouth
6.5 - 7.5
pH of duodenum
7-8.5
Main function of gut microbes
Metabolise undigested dietary components, e.g. fibre which is not digested in stomach/SI
3 ways gut microbes can defend against pathogens
Acting as a barrier - to prevent pathogen colonisation
Active competitive exclusion - commensal bacteria can produce active compounds to kill pathogens
pH inhibition - pathogens generally grow best at ph>6, proximal colon has pH 5.5 but distal colon pH 6.5
More risk of pathogen colonisation in proximal or distal colon + why
proximal colon has pH 5.5 but distal colon usually pH 6.5 so MORE RISK OF PATHOGEN COLONISATION IN DISTAL COLON as pathogens grow best at ph>6
Functions of bacteria in the GI tract (6)
Metabolise undigested dietary components Defend against pathogens Produce essential metabolites, e.g. short chain fatty acids Modify host secretions, e.g. bile Develop immune system Control host signalling
Function of E. rectale & F. prausnitzii
Produce butyrate ( a SCFA)
Function of megasphaera
Produce propionate ( a SCFA)
Function of bactericides
Utilise acetate
Functions of bifidobacteria (2)
Utilise prebiotics
Produce lactate
Functions of lactobacilli (2)
Produce lactic acid
Degrade mucin
High bacterial diversity is a biomarker of what
Good health
Products of microbial fermentation (5)
Short chain fatty acids/ branched chain fatty acids Phytochemicals Gases - CO2, H2, CH4 Other metabolites Minerals
3 main short chain fatty acids from carbohydrate metabolism
Butyrate
Proprionate
Acetate
Function of butyrate (a SCFA)
involved in epithelial cell growth
Function of propionate
involved in gluconeogenesis
Function of acetate
transported in blood to peripheral tissues, involved in lipogenesis
Rate of butyrate:propionate:acetate
1:1:3
Bacterial in proximal colon ferment more carbohydrate/protein while bacteria in distal colon ferment more carbohydrate/protein
Carbohydrate
Protein
Dysbiosis of gut microbiotia disrupts what which leads to what
Disrupts homeostasis –> gut inflammation
Dietary fibre improves what
Faecal bulking resulting in shorter transit time in colon
Fermentation of fibre by bacteria leads to what
Release of additional phytochemicals
Maintains acidic pH - to resist pathogens
Increases commensal bacteria
Essential supply of SCFAs
Babies have low or high bacterial diversity
Low
Difference between causation and correlation with respect to microbes and disease
Microbial dysbiosis could be a cause of gut disease but it could also be the gut disease that’s causing microbial dysbiosis
Name some infections/disease that are caused by microbial dysbiosis (i.e. usually these bacteria live asymptomatically) (4)
MRSA (Staph aureus) infection
Streptococcus throat infection
C. diff infection
Gastritis/ Gastric cancer- H.pylori
Inflammation in IBD is most likely due to what in regards to microbiota and immune response
Dysregulated immune response to gut microbiota
Evidence has shown that there’s reduced bacterial diversity in crohn’s or UC
Crohn’s
In crohn’s there may be elevated levels of what type of bacteria
Enterobacteriaceae
How do features of IBD itself have an impact on microbiota (4)
Antibiotic use - reduces bacterial diversity
Inflammation - decreases mucus barrier –> more oxygen exposure –> changes microbial composition
Diarrhoea - decreased transit time altering microbial composition
Diet - desire to eat less fibre –> changes microbial composition
Effect of antibiotics on gut microbiota
Reduce bacterial diversity
-creates selection pressure (loss of diverse bacteria, left with just a few species) resulting in the increase and spread of a bacterial resistance
Effect of broad spectrum antibiotics on bacteria
kill pathogenic bacteria AND kill many of the commensal, resident bacteria that may be important for health
What are probiotics
live micro-organisms conferring health benefit when administered adequately, e.g. Bifidobacterium
Frequent functions of probiotics (3)
Bioconversion
Antagonistic to pathogens
Stimulate immune system
What are probiotics
substrate used by host bacteria (food for bacteria) conferring health benefit, e.g. garlic
Probiotics can potentially be used to treat what disease
reduce incidence of C. diff associated diarrhoea
How may prebiotics may be helpful in IBD
IBD to boost numbers of Faecalibacterium prausnitzii so enhancing production of anti-inflammatory protein and reducing effects of IBD
Function of Faecalibacterium prausnitzii (F. prausnitzi)
production of anti-inflammatory protein
Potential functions of prebiotics (4)
Improve gut function by increasing faecal bulk
Reduce risk of colon cancer by reducing DNA damage
Used in infant formula to increase bifidobacteria numbers
Increase calcium absorption
Explain why FMT (faecal microbial transplantation) may be more effective in treating recurrent C. difficile infection than other GI diseases
Faecal sample from healthy donor transplanted and repopulates microbiota of colon, displacing C. diff and preventing re-infection
may not work in other GI diseases because success depends on whether any microbiota is present/absent
-In c. diff infection, majority of microbiota is destroyed which allows FMT to work
